He became known as Badwater Bart. Overcoming a fear of public speaking, he became an in-demand celebrity performer. But it wasn't just race directors around the country calling him, it was race directors around the world. He ran in India and Africa. He considered the race in South Africa again—the one that made mere marathons seem like childish larks, and he thought, someday, when he wasn't so busy. He had all the time in the world. He ran at a nudist camp and he organized a race for recovering drug addicts. Neither their rough backgrounds nor the yammering voices in their heads had stopped them from working toward meaningful lives. He felt a bond with them.

Life had thrown a lot of things at him, too, but he had endured them all, had used them to grow faster and stronger. And then, there was something he couldn't beat with sheer willpower. In 1991, after the Lake Waramaug 50-miler in Connecticut, he could barely get out of bed. He thought it was the flu. He went to a doctor who told him to rest up. Weeks later, he went back and the doctor performed some tests and told him he had Lyme disease, and put him on a course of oral antibiotics.

Yasso stepped it up. He organized races; he raced 10-Ks, and marathons, and ultras. Those were his glory years, from 1991 to 1997. He rode his bike 25 miles to work, and 25 miles back, except on Thursdays. That's when he covered the same course on foot. "Running is good," he says, referring to that period of his life. "Life is good. Job is good. It's all good."

He knew—and knows—that part of his good fortune was luck. "By some genetic twist," he writes, "I had been given a body that was indefatigable."

It was exactly that apparent invulnerability to exhaustion that almost proved his undoing.

It was June 1997, and he was six miles from the top of Mount Kilimanjaro, on the third day of a four-day group trek up the mountain. The previous week he had flown 12 hours from New York City to Cairo with a friend, and while in that city had awakened in his hotel room sweating profusely and shaking with chills. "I did what I always do when I'm feeling out of sorts," he writes. "I went for a run."

He felt better afterward—he always did—and after flying to Nairobi, then riding a bus for eight hours into Tanzania, he started hiking. The morning of the second day, he had a hard time breathing, and his legs burned. He blamed the altitude—9,000 feet. The next morning, his legs hurt worse, and he had developed a rash on his arms and chest. He kept going. The third day, the vision in his right eye was blurry, and then he couldn't close it. When he got out of bed, he pitched over. The right side of his face was paralyzed. After a nine-mile trudge to the bottom of the mountain, and a cab ride to a one-room concrete outpost where steel bars covered the pharmacy, and another eight-hour bus ride, he ended up in a Nairobi hospital. His fever was back, "one eyelid was frozen open, and the right side of my face drooped. The glands in my throat were so swollen that I hadn't eaten anything for three days."